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SUMMARY:Light-matter interaction in atomically thin semiconductors: darkne
 ss\, brightness\, spins and valleys - Dr. Bernhard Urbaszek\, CNRS – Tou
 louse University\, France
DTSTART:20180319T153000Z
DTEND:20180319T163000Z
UID:TALK103192@talks.cam.ac.uk
CONTACT:Dr Ulrich Schneider
DESCRIPTION:Transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2
  are layered materials that are semiconductors with a direct bandgap when 
 thinned down to one monolayer. Despite an incredible number of results pub
 lished in the field since 2010\, many basic parameters such as the effecti
 ve carrier mass are not experimentally determined – which leaves plenty 
 of room for further exploration of these fascinating materials. Even sampl
 es exfoliated in ambient conditions with simple scotch-tape methods show r
 emarkable properties for optoelectronics and spintronics: TMDC monolayers 
 strongly interact with light in the visible region of the optical spectrum
 . The optically generated electrons and holes form excitons with high bind
 ing energy (several hundred meV) and high oscillator strength\, resulting 
 in optical absorption up to 20 % per monolayer. Interband optical selectio
 n rules are polarization selective (chiral). This allows addressing non-eq
 uivalent valleys in momentum space with polarized lasers for optical spin 
 and valley index manipulation.\nWe access the optical and spin properties\
 , studying valley dynamics for different exciton species and resident carr
 iers\, with unprecedented detail in TMDC monolayers sandwiched between ult
 rathin insulating layers of hexagonal boron nitride (hBN) in van der Waals
  heterostructures. The optical emission of these encapsulated monolayers i
 s spectrally narrow (down to 1 nm FWHM) comparable to emission from III-V 
 quantum well structures used in today’s optoelectronic devices and appro
 aching the homogenous limit. This insight paves the way for integrating TM
 DCs in photonic devices and ferromagnetic- semiconductor heterostructures.
LOCATION:Ryle Seminar Room (930) 
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